FAQs

Deployment

How to select hardware and optimize configuration

Hardware Selection

  • For BE, we recommend 16 cores with 64GB or more. For FE, we recommend 8 cores with 16GB or more.
  • HDDs or SSDs can be used.
  • CPU must support AVX2 instruction sets, use cat /proc/cpuinfo |grep avx2 to confirm there is output. If not, we recommend replacing the machine. StarRocks' vectorization engine needs CPU instruction sets to perform a better effect.
  • The network needs 10 GB NIC and 10 GB switch.

Modeling

Partitioning and bucketing

Range partitioning

  • Reasonable range partitioning can reduce the amount of data for scanning. Taking a data management perspective, we normally choose “time” or “region” as range partition keys.
  • With dynamic partitioning, you can create partitions automatically at regular intervals (on a daily basis).

Hash partitioning

  • Choose high-cardinality columns as the hash partition key) to ensure that data is balanced among buckets. If a column has a unique ID, use it as the hash partition key. If there is data skew, use multiple columns as the hash partition key but try not to choose too many columns.
  • The number of buckets affects query parallelism. We recommend setting each bucket around 100MB to 1GB.
  • To make full use of the limited machine resources, set the number of buckets based on Number of BE * cpu core / 2. For example, you have a table with 100GB data and four BEs each of which is 64C. To take full advantage of the CPU resources with only one partition, you can set 144 buckets (4 * 64 /2 = 144) and each bucket contains 694 MB data.

Sort key

  • Design the sort key based on your query needs.
  • To speed up queries, choose columns that are often used as filter and group by conditions as sort keys.
  • If there is a large data-point query, we recommend you to put the query ID in the first column. For example, if the query is select sum(revenue) from lineorder where user_id='aaa100'; and there is high concurrency, we recommend putting user\_id as the first column of the sort key.
  • If the query is mainly aggregation and scan, we recommend putting the low-cardinality columns first. For example, if the main type of query is select region, nation, count(*) from lineorder_flat group by region, nation, it would be more appropriate to put region as the first column and nation as the second. Putting the low-cardinality columns in front achieves data locality.

Data types

  • Choose precise data types. In other words, don't use string if you can use int; don't use bigint if you can use int. Precise data types help the database perform better.

Query

Query parallelism

  • Set the query parallelism via the session variable parallel\_fragment\_exec\_instance\_num. If the query performance is not satisfying but CPU resources are sufficient, adjust the parallelism by setting parallel\_fragment\_exec\_instance\_num = 16;. Parallelism can be set to half the number of CPU cores .
  • To make the session variable globally valid, setglobal parallel\_fragment\_exec\_instance\_num = 16;.
  • parallel\_fragment\_exec\_instance\_num is affected by the number of tablets owned by each BE. For example, if a table has 32 tablets and 3 partitions distributed on 4 BEs, then the number of tablets per BE is 32 * 3 / 4 = 24. In this case, the parallelism value of each BE cannot exceed 24. Even if you set parallel\_fragment\_exec\_instance\_num = 32, the parallelism value will still be 24 during execution.
  • To process high QPS queries, we recommend setting parallel\_fragment\_exec\_instance\_num to 1. This reduces the competition for resources during querying and therefore improves the QPS.

Use profile to analyze query bottlenecks

  • To view the query plan, use the command explain sql.
  • To enable profile reporting, set is\_report\_success = true.
  • To view the current query and profile information, go to http:FE\_IP:FE\_HTTP\_PORT/queries.